JP2018037189A - Method for manufacturing negative electrode for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a battery, which is improved in charge and discharge characteristics.SOLUTION: A method for manufacturing a negative electrode for a battery comprises the steps of: (A) preparing a first mixture material by mixing negative electrode active material particles and an ammonium polycarboxylate; (B) preparing a second mixture material by mixing conductive material particles and an ammonium polycarboxylate; (C) preparing a third mixture material by mixing the first mixture material, the second mixture material and solvent; (D) preparing a fourth mixture material by mixing the third mixture material and a binder; and (E) putting the fourth mixture material on a surface of current collector foil.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a method for producing a negative electrode for a battery.

  Japanese Patent Application Laid-Open No. 2012-059722 (Patent Document 1) discloses forming an active material layer containing active material particles and a binder after supporting a conductive material on the surface of the active material particles.

JP 2012-059722 A

  Conventionally, a negative electrode for a battery (hereinafter sometimes abbreviated as “negative electrode”) is manufactured by arranging a composite material containing negative electrode active material particles and a binder on the surface of a current collector foil. The composite material is prepared by mixing negative electrode active material particles, a binder, and the like.

  In order to improve the charge / discharge characteristics of the negative electrode, conductive material particles such as carbon black have been studied. However, since conductive material particles such as carbon black have a large surface area, they tend to aggregate. When the conductive material particles aggregate, the conductive path is easily interrupted and it is difficult to form a wide conductive network.

  In Patent Document 1, a compound to be a conductive material is supported on active material particles. According to this aspect, since the conductive material hardly aggregates, it is expected that a negative electrode in which the conductive material is uniformly distributed is formed. However, when the composite material is prepared or when the composite material is disposed on the surface of the current collector foil, a large shear stress is applied to the active material particles. Therefore, the conductive material may be peeled off from the active material particles. When the conductive material is peeled from the active material particles, the conductive network is interrupted and desired charge / discharge characteristics cannot be obtained.

  Therefore, an object of the present disclosure is to provide a negative electrode for a battery having improved charge / discharge characteristics.

  Hereinafter, the technical configuration and operational effects of the present disclosure will be described. The mechanism of action of the present disclosure includes estimation. Therefore, the scope of the invention of the present disclosure should not be limited by the correctness of the action mechanism.

The manufacturing method of the negative electrode for a battery according to the present disclosure includes the following (A) to (E).
(A) A first composite material is prepared by mixing negative electrode active material particles and ammonium polycarboxylate.
(B) The second composite material is prepared by mixing the conductive material particles and ammonium polycarboxylate.
(C) A 3rd compound material is prepared by mixing a 1st compound material, a 2nd compound material, and a solvent.
(D) A 4th compound material is prepared by mixing a 3rd compound material and a binder.
(E) A negative electrode for a battery is manufactured by disposing the fourth composite material on the surface of the current collector foil.

  In the production method of the present disclosure, polycarboxylate ammonium salt (PCA) is used. PCA has the unique property of responding to pressure. In other words, PCA is a pressure responsive polymer.

  In the production method of the present disclosure, first, as shown in the above (A) and (B), the first composite material and the second composite material are separately prepared. In the first composite material, PCA adheres to the surface of the negative electrode active material particles. In the second composite material, PCA adheres to the surface of the conductive material particles. Thereafter, as shown in (C) above, the first composite material, the second composite material, and the solvent are mixed to prepare the third composite material.

  FIG. 1 is a conceptual diagram illustrating the operation of PCA. PCA 3 is attached to the surface of the negative electrode active material particles 1 and the surface of the conductive material particles 2, respectively. At normal pressure, PCA3 has a high degree of dissociation. Therefore, PCA3 has a polymer chain extended and is negatively charged. Therefore, the negative electrode active material particles 1 and the conductive material particles 2 are uniformly dispersed. That is, aggregation of the conductive material particles 2 is suppressed.

  By mixing the first composite material, the second composite material, and the solvent, shear stress is applied to the PCA 3. That is, the PCA 3 is pressurized. By pressurization, the degree of dissociation of PCA3 decreases and the polymer chain contracts. When the PCA 3 contracts, portions where the PCA 3 is not attached are exposed on the surface of the negative electrode active material particles 1 and the surface of the conductive material particles 2. Thereby, the negative electrode active material particles 1 and the conductive material particles 2 aggregate. Furthermore, the negative electrode active material particles 1 and the conductive material particles 2 are firmly bonded due to the entanglement of the polymer chains. Thereby, a strong conductive path is formed between the negative electrode active material particles 1 and the conductive material particles 2. Therefore, in the subsequent mixing with the binder ((D) preparation of the fourth composite material) and arrangement on the surface of the current collector foil ((E) production of the battery electrode), the conductive material particles 2 are the negative electrode active material particles 1. It is suppressed that it peels off from.

  As a result, in the negative electrode for a battery, a wide and strong conductive network is formed by continuous conductive paths. Thereby, it is thought that the charging / discharging characteristic of the negative electrode for batteries improves.

FIG. 1 is a conceptual diagram illustrating the action of ammonium polycarboxylate. FIG. 2 is a flowchart illustrating an outline of a method for manufacturing a negative electrode for a battery according to an embodiment of the present disclosure.

  Hereinafter, an embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of the present disclosure.

<Method for producing negative electrode for battery>
In the manufacturing method of the present embodiment, a negative electrode for a lithium ion secondary battery is typically manufactured. However, the negative electrode manufactured by the manufacturing method of this embodiment is not necessarily limited to the negative electrode for lithium ion secondary batteries.

  The negative electrode manufactured according to this embodiment has improved charge / discharge characteristics. Therefore, the negative electrode manufactured according to this embodiment is suitable for applications that require extremely high charge / discharge characteristics. As such an application, for example, an in-vehicle power supply can be cited. However, the use of the negative electrode manufactured according to this embodiment is not limited to in-vehicle use. The negative electrode manufactured by this embodiment is applicable to all uses.

  FIG. 2 is a flowchart showing an outline of a method for producing a negative electrode for a battery according to this embodiment. The manufacturing method of this embodiment includes (A) preparation of the first composite material, (B) preparation of the second composite material, (C) preparation of the third composite material, (D) preparation of the fourth composite material, and ( E) Includes production of negative electrodes for batteries. Hereinafter, the manufacturing method of this embodiment will be described in order.

<< (A) Preparation of the first composite material >>
The manufacturing method of this embodiment includes preparing a 1st compound material by mixing (A) negative electrode active material particles and ammonium polycarboxylate.

(Negative electrode active material particles)
The negative electrode active material particles are not particularly limited as long as they are particles that function as the negative electrode active material of the battery. The negative electrode active material particles may be carbon particles such as graphite, graphitizable carbon and non-graphitizable carbon, or may be metal particles such as silicon and tin.

  The negative electrode active material particles have an average particle diameter of about 1 to 20 μm, for example. The average particle size in the present specification indicates a particle size of 50% cumulative from the fine particle side in the volume-based particle size distribution measured by the laser diffraction scattering method.

(Ammonium polycarboxylate)
The ammonium polycarboxylate (PCA) of this embodiment is a polymer represented by the following structural formula (I), for example. In the following structural formula (I), n represents an integer of 10 or more.

PCA has pressure responsiveness. PCA has a high degree of dissociation at normal pressure. That is, most of “—COONH ₄ ” in the polymer chain is dissociated into “—COO ⁻ (carboxylate anion)”. Therefore, at normal pressure, the polymer chain of PCA is elongated and is negatively charged. At normal pressure, PCA attached to the surface of the negative electrode active material particles and the surface of the conductive material particles described later exhibits an action of dispersing them.

  When PCA is pressurized, the degree of dissociation decreases and contracts. Moreover, PCA becomes hydrophobic due to a decrease in the degree of dissociation. Therefore, the PCA adhered to the surface of the negative electrode active material particles and the surface of the conductive material particles during pressurization exhibits an action of aggregating them. In the manufacturing method of this embodiment, a strong conductive network is formed by the unique action of this PCA.

  A general stirring device can be used for mixing the negative electrode active material particles and the PCA. For example, an agitation device having a disk turbine can be used. During mixing, the PCA is typically supplied in the form of an aqueous solution. The PCA aqueous solution has a concentration of 30 to 60% by mass, for example. By mixing the negative electrode active material particles and the PCA aqueous solution, PCA adheres to the surface of the negative electrode active material particles.

  In the present embodiment, the PCA adhesion amount is expressed as a mass ratio of PCA to the mass of the negative electrode active material particles. The amount of PCA attached to the negative electrode active material particles is preferably 0.2% by mass or more and 0.6% by mass or less. When the PCA adhesion amount to the negative electrode active material particles is 0.2% by mass or more, it is easy to obtain a binding action due to entanglement of polymer chains. When the PCA adhesion amount to the negative electrode active material particles is 0.6% by mass or less, the surface of the negative electrode active material particles is easily exposed when the PCA contracts. Thereby, the improvement of charging characteristics is expected.

<< (B) Preparation of 2nd compound material >>
The manufacturing method of this embodiment includes preparing a 2nd compound material by mixing (B) electroconductive material particle and polycarboxylate ammonium.

(Conductive material particles)
The conductive material particles should not be particularly limited as long as they are particles having electronic conductivity. The conductive material particles may be carbon black such as acetylene black, thermal black, and furnace black. The conductive material particles are, for example, about 1 to 20% by mass with respect to the mass of the negative electrode active material particles.

  A general stirring device can also be used for mixing the conductive material particles and the PCA. By mixing the conductive material particles and the aqueous PCA solution, PCA adheres to the surface of the conductive material particles.

  In general, the conductive material particles have a larger surface area than the negative electrode active material particles. Therefore, the conductive material particles tend to aggregate more easily than the negative electrode active material particles. Therefore, it is preferable that the amount of PCA attached to the conductive material particles is larger than the amount of PCA attached to the negative electrode active material particles. Thereby, the dispersibility of electroconductive material particle improves and the improvement of a charge / discharge characteristic is anticipated. Of course, this is not the case when the conductive material particles have a surface area equal to or less than the surface area of the negative electrode active material particles.

  The amount of PCA attached to the conductive material particles is preferably 0.6% by mass or more and 1.0% by mass or less. When the PCA adhesion amount to the conductive material particles is 1.0% by mass or less, the surface of the conductive material particles is easily exposed when the PCA contracts. Thereby, it is expected that a good conductive path is formed between the negative electrode active material particles and the conductive material particles. The total of the amount of PCA attached to the negative electrode active material particles and the amount of PCA attached to the conductive material particles is preferably 0.8% by mass or more and 1.6% by mass or less.

<< (C) Preparation of third composite material >>
The manufacturing method of this embodiment includes preparing the 3rd compound material by mixing the (C) 1st compound material, the 2nd compound material, and a solvent.

  The solvent may be water, for example. For the mixing of the first composite material, the second composite material and the solvent, for example, a stirring granulator can be used. Mixing is performed so that shear stress is applied to the PCA. When shear stress is applied to the PCA, the PCA contracts, and the negative electrode active material particles and the conductive material particles are combined.

  The shear stress can be adjusted by, for example, the shape of the stirring blade, the rotation speed of the stirring blade, the solid content ratio of the composite material, and the like. A solid content rate shows the mass ratio of components other than a solvent. The final solid content ratio of the composite material (the solid content ratio of the fourth composite material described later) can be determined based on, for example, the solid content ratio that maximizes the torque required for mixing. The solid content (mass%) is, for example, (X-12) or more and X or less. Here, “X (mass%)” indicates the solid content ratio that maximizes the torque required for mixing.

  When the fourth composite material is prepared as a paint, the solid content is, for example, about 50 to 60% by mass. The fourth composite material may be prepared as a wet powder. When the fourth composite material is prepared as a wet powder, the solid content is, for example, about 70 to 80% by mass.

<< (D) Preparation of fourth composite material >>
The manufacturing method of the present embodiment includes (D) preparing the fourth composite material by mixing the third composite material and the binder.

(Binder)
The binder should not be particularly limited. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or the like. A binder is about 0.1-2 mass% with respect to the mass of negative electrode active material particle, for example. An agitation granulator can also be used for mixing the third composite material and the binder.

<< (E) Production of negative electrode for battery >>
The manufacturing method of this embodiment includes manufacturing the negative electrode for batteries by arrange | positioning (E) 4th compound material on the surface of current collection foil.

  The current collector foil may be, for example, a copper (Cu) foil. When the fourth composite material is made into a paint, the fourth composite material can be applied to the surface of the current collector foil by, for example, a die coater. When the fourth composite material is a wet powder, the fourth composite material can be disposed on the surface of the current collector foil by, for example, a roll coater. Thereby, a negative electrode is manufactured. The negative electrode can be rolled to a predetermined thickness and cut into a predetermined dimension according to the battery specifications.

  Examples will be described below. However, the following examples do not limit the scope of the invention of the present disclosure.

<Manufacture of negative electrode for battery>
Negative electrodes according to Examples and Comparative Examples were manufactured as follows.

Example 1
The following materials were prepared:
Negative electrode active material particles: Graphite Conductive material particles: Acetylene black Ammonium polycarboxylate aqueous solution (concentration: about 40 mass%)
Solvent: Water Current collector foil: Cu foil (thickness: 10 μm)

(A) Preparation of 1st compound material The negative electrode active material particle and PCA aqueous solution were mixed with the disper. Thereby, the 1st compound material was prepared. The number of revolutions of the disper was 3000 rpm. The amount of the PCA aqueous solution was adjusted so that the PCA was 0.4% by mass with respect to the negative electrode active material particles. In the first composite material, PCA is considered to adhere to the surface of the negative electrode active material particles.

(B) Preparation of 2nd compound material Conductive material particle and PCA aqueous solution were mixed with the disper. Thereby, the 2nd compound material was prepared. The number of revolutions of the disper was 3000 rpm. The amount of the PCA aqueous solution was adjusted so that PCA was 1.0 mass% with respect to the negative electrode active material particles. In the second composite material, PCA is considered to be attached to the surface of the conductive material particles.

(C) Preparation of 3rd compound material The 1st compound material, the 2nd compound material, and the solvent were mixed with the stirring granulator. Thereby, the 3rd compound material was prepared. The amount of the solvent was adjusted so that the solid content of the fourth composite material was 56% by mass.

(D) Preparation of 4th compound material The 3rd compound material and the binder were mixed with the stirring granulator. Thereby, the 4th compound material (negative electrode coating material) was prepared. The amount of the binder was 0.7% by mass with respect to the negative electrode active material particles.

(E) Manufacture of battery negative electrode A fourth composite material (negative electrode composite paint) was applied to the surface of the current collector foil by a die coater and dried. Thereby, the 4th compound material was arranged on the surface of current collection foil. The negative electrode mixture and the current collector foil were rolled and cut so as to have predetermined dimensions. From the above, the negative electrode (strip-shaped sheet) according to Example 1 was manufactured. The dimensions of the negative electrode are as follows.

Thickness: 80μm
Total length: 3300mm
Full width: 120mm
Negative electrode composite width: 100 mm

<Manufacture of batteries>
A lithium ion secondary battery having a rated capacity of 4 Ah was manufactured as follows.

1. Preparation of positive electrode The following materials were prepared.
Positive electrode active material particles: lithium nickel cobalt manganese composite oxide Conductive material particles: acetylene black Binder: polyvinylidene fluoride Solvent: N-methyl-2-pyrrolidone Current collector foil: aluminum foil (thickness 20 μm)

  The positive electrode mixture paint was prepared by mixing the positive electrode active material particles, the conductive material particles, the binder, and the solvent. The conductive material particles were 8% by mass with respect to the mass of the positive electrode active material particles. The binder was 2% by mass with respect to the mass of the positive electrode active material particles. The positive electrode mixture paint was applied to the surface of the current collector foil by a die coater and dried. Thereby, the positive electrode mixture was disposed on the surface of the current collector foil. Furthermore, the positive electrode mixture and the current collector foil were processed into predetermined dimensions. From the above, a positive electrode (strip-shaped sheet) was produced. The dimensions of the positive electrode are as follows.

Thickness: 70 μm
Total length: 3000mm
Full width: 114mm
Width of positive electrode mixture: 94mm

2. Production of Separator A separator substrate having a thickness of 20 μm was prepared. This separator substrate is constituted by laminating a polypropylene porous layer, a polyethylene porous layer, and a polypropylene porous layer in this order.

  A paint was prepared by mixing alumina particles, an acrylic binder and a solvent. For the mixing, a disperser “CLEAMIX” manufactured by M Technique was used. The paint was applied to the surface (one side) of the separator substrate. A gravure coater was used for coating. As a result, a heat-resistant layer having a thickness of 5 μm was formed. From the above, a separator was produced.

3. Configuration of electrode group The positive electrode, the separator, and the negative electrode were wound to form an electrode group. The separator was disposed between the positive electrode and the negative electrode so that the heat-resistant layer was opposed to the negative electrode. Furthermore, a predetermined current collecting terminal was attached to the electrode group.

4). Production of Battery An electrolytic solution having the following composition was prepared.
1 mol / l LiPF ₆ , EC: DMC: EMC = 3: 4: 3 (v: v: v)
Here, EC represents ethylene carbonate, DMC represents dimethyl carbonate, and EMC represents ethyl methyl carbonate.

  A square battery case was prepared. The electrode group was accommodated in the battery case. A predetermined amount of electrolyte was injected into the battery case. The battery case was sealed. Thus, a battery was manufactured.

5. Initial charge / discharge In a 25 ° C environment. The battery was charged with 4 A current until it reached 4.1V. Thereafter, the battery was discharged at a current of 4 A until it reached 3.0 V. The discharge capacity at this time was set as the initial capacity.

<< Examples 2-8 and 11-13 >>
As shown in Table 1 below, Examples 2 to 8 and 11 to 13 are performed in the same procedure as Example 1 except that the amount of PCA in the first compound and the second compound is changed. Such a negative electrode and a battery were produced.

<< Examples 9, 10 and 14 >>
As shown in Table 1 below, negative electrodes and batteries according to Examples 9, 10 and 14 were manufactured by the same procedure as Example 1 except that the solid content ratio was changed.

<< Comparative Example 1 >>
A negative electrode and a battery according to Comparative Example 1 were produced by the same procedure as Example 1 except that carboxymethylcellulose (CMC) was used instead of PCA.

<< Comparative Example 2 >>
The negative electrode active material particles, the conductive material particles, the PCA aqueous solution, the solvent, and the binder were mixed together to prepare a negative electrode mixture paint. Except for this, a negative electrode and a battery according to Comparative Example 2 were manufactured by the same procedure as in Example 1. The composition of each component in the negative electrode of Comparative Example 2 is the same as in Example 1.

<< Comparative Example 3 >>
The first composite material was prepared by mixing the negative electrode active material particles and PCA. The first composite material, the conductive material particles, the solvent and the binder were mixed to prepare a negative electrode composite paint. Except for this, a negative electrode and a battery according to Comparative Example 3 were manufactured by the same procedure as in Example 1. The composition of each component in the negative electrode of Comparative Example 3 is the same as in Example 1.

<< Comparative Example 4 >>
The second composite material was prepared by mixing the conductive material particles and PCA. By mixing the second composite material, the negative electrode active material particles, the solvent and the binder, a negative electrode composite coating material was prepared. Except for this, a negative electrode and a battery according to Comparative Example 4 were produced by the same procedure as in Example 1. The composition of each component in the negative electrode of Comparative Example 4 is the same as in Example 1.

<Evaluation>
1. Evaluation of discharge characteristics Discharge characteristics were evaluated by a discharge test at room temperature.
The battery voltage was adjusted to 3.7V. In a 25 ° C. environment, the battery was discharged for 10 seconds with a current of 40 A. The amount of voltage drop during discharge was measured. The initial resistance was calculated by dividing the voltage drop by the discharge current. The results are shown in Table 1 below. The lower the initial resistance, the better the discharge characteristics.

2. Evaluation of charging characteristics Charging characteristics were evaluated by a cycle test at a low temperature.
The battery voltage was adjusted to 3.7V. The battery was placed in a thermostat set to −10 ° C. The following operation of “charge → pause → discharge → pause” was defined as one cycle, and the operation was performed 1000 cycles.

Charging: 8A x 20 seconds Pause: 5 minutes Discharge: 8A x 20 seconds Pause: 5 minutes

  After 1000 cycles, the post-cycle capacity was measured under the same conditions as the initial capacity. The capacity retention rate was calculated by dividing the capacity after the cycle by the initial capacity. The results are shown in Table 1 below. The higher the capacity retention rate, the better the charging characteristics (Li acceptability).

<Result>
Comparative Example 1 has low charging characteristics. It is considered that CMC does not have an effect of increasing the dispersibility of the conductive material particles.

  Comparative Examples 2 to 4 have low discharge characteristics. From this result, it is understood that it is important to attach PCA to each of the surface of the negative electrode active material particles and the surface of the conductive material particles.

  In Examples 1 to 14, the charge / discharge characteristics are improved as compared with Comparative Examples 1 to 4. Since PCA is attached to each of the surface of the negative electrode active material particles and the surface of the conductive material particles, the action of the PCA to improve the dispersibility of the conductive material particles, and between the negative electrode active material particles and the conductive material particles It is considered that the action of forming a strong conductive path was exhibited.

  From the results of Example 7 and Example 12, it can be seen that the charge / discharge characteristics are further improved when the amount of PCA attached to the conductive material particles is larger than the amount of PCA attached to the negative electrode active material particles. It is considered that the dispersibility of the conductive material particles is improved.

  Example 11 has lower charge / discharge characteristics than Examples 1-10. Since PCA is excessive, it is considered that the exposed surface is reduced in the negative electrode active material particles and the conductive material particles, and the resistance is increased.

  Example 13 has lower charge / discharge characteristics than Examples 1-10. Since PCA is too small, the effect of improving the dispersibility of the conductive material particles is small, and the conductive path between the negative electrode active material particles and the conductive material particles is considered to be slightly weak.

  From the results of Examples 1 to 10, the PCA adhesion amount to the negative electrode active material particles is preferably 0.2% by mass or more and 0.6% by mass or less, and the PCA adhesion amount to the conductive material particles is preferably 0%. It is considered that it is from 6% by mass to 1.0% by mass.

  From the results of Example 1, Example 9, Example 10, and Example 14, it can be seen that the improvement width of the charge / discharge characteristics varies depending on the solid content rate. It is considered that the shear stress (that is, the pressure) at the time of mixing changes depending on the solid content, and thus the pressure response of PCA also changes.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 Negative electrode active material particles, 2 conductive material particles, 3 PCA (ammonium polycarboxylate).

Claims (1)

Preparing a first composite material by mixing negative electrode active material particles and ammonium polycarboxylate;
Preparing a second composite by mixing conductive material particles and ammonium polycarboxylate;
Preparing a third composite by mixing the first composite, the second composite and a solvent;
Preparing a fourth composite material by mixing the third composite material and a binder, and producing a negative electrode for a battery by disposing the fourth composite material on a surface of a current collector foil;
The manufacturing method of the negative electrode for batteries containing this.

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